The present invention relates to the field of data communications; more particularly, the present invention relates to performing automatic repeat request (ARQ) sessions in a communication system.
A communication system transfers information between a source and a destination. Generally, a communication system includes a transmitter and a receiver which transmit and receive information signals over some media. This media may be cable wiring or atmosphere. When communications occur over atmosphere, or airwaves, they are commonly referred to as xe2x80x9cwirelessxe2x80x9d communications. Examples of wireless communication systems include digital cellular, packet data, paging and digital cordless telephones, wireless modems, wireless local and wide area networks, digital satellite communications and personal communications networks.
Paging communication systems have typically been one-way communication systems. Recently, two-way paging systems have been introduced and are now commercially available.
One problem faced with current wireless communications systems is ensuring that the entire message is received by the mobile unit without errors. Some communication systems perform ARQ, or Automatic Repeat reQuest, as a way of providing reliable transmission of information over a lossy channel. In all ARQ schemes, the sender and recipient communicate with each other so that when some data arrives at the recipient having been corrupted or is lost, the sender retransmits that information until either the entire message is received reliably by the recipient or the message transfer is aborted.
ARQ has been used in wired communications systems in the prior art. More recently, ARQ has been used in GSM and cellular. For example, see the TIA/EIA interim standard, TIA/EIA/IS-136.2-A, October 1996 for cellular communication. However, the IS-136 implements symmetric forward and reverse channels and each unit is autonomously responsible for its own timing and actions.
Two-way paging channels have the characteristic of non-real time operation, limited reverse channel bandwidth (when compared to the forward channel), and the network device, or terminal, controls the allocation of the bandwidth.
When an ARQ session is started, there is no guarantee that the receiving unit will receive the entire message. The receiving unit may end up with a message with errors. This situation leads to another problem in that even if the receiving unit won""t be able to receive the entire message without errors, the receiving unit is still consuming valuable battery power in the process. It would be desirable to ensure that messages, once started, are received without errors and that no extraneous power consumption due to extraneous transmissions occurs.
In Forward Channel ARQ, because the ARQ message is sent in separately transmitted fragments, the device receiving the ARQ message may not be able to receive the entire message. This is because the receiving unit cannot determine whether it has enough memory to receive the entire ARQ message before some portion of the message is already received. Also the receiving unit cannot refuse an ARQ message.
In the Reverse Channel ARQ, once the system knows that a mobile unit wants to send a message, the transmissions are scheduled and an acknowledgment is sent by the network unit after receiving each fragment. Thus, the network unit knows when the message has been sent completely. If the network unit does not receive a scheduled transmission, it sends a message requesting the mobile unit to resend the last transmission. The mobile unit responds by transmitting the last fragment (that it understood was to be sent).
One problem associated with Reverse Channel ARQ is that after the network unit has indicated that the entire message has been received (because it knows when the entire message has been received), it sends the acknowledgment to the mobile unit. However, if the mobile unit does not receive this acknowledgment from the network unit, it will continue sending the final fragment. However, the network unit, operating as it had already received the entire message, is no longer looking for the last fragment from the mobile unit and, as far as it is concerned, believes that the ARQ session has ended. Therefore, the mobile unit will continue to send the last fragment, thereby consuming extra energy in continuing to transmit and continuing to wait for the network unit""s acknowledgment, even though the message has been completed or has been completely received by the network unit. It would be desirable to avoid this extra power consumption and ensure that both units know that the ARQ session has been completed successfully.
The present invention provides for performing ARQ in a manner that avoids the problems and limitations described above in the prior art.
Forward and Reverse Channel Automatic Repeat reQuest (ARQ) communication methods and systems are described. The present invention provides a system having a mobile unit and a network terminal for two way communication with the mobile unit using forward and reverse channels with the network terminal controlling the timing and bandwidth allocation for the reverse channel.
This invention also provides a selective call receiver comprising a storage space and control operable to refuse to receive a message when available space in the storage space is not large enough to store the message.